feat(jsx-email)!: add --exclude flag to preview

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Component / Package Name:

This PR contains:

• [ ] bugfix
• [x] feature
• [ ] refactor
• [ ] documentation
• [ ] other

Are tests included?

• [x] yes (bugfixes and features will not be merged without tests)
• [ ] no

Breaking Changes?

• [x] yes (breaking changes will not be merged unless absolutely necessary)
• [ ] no

If yes, please include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

This PR adds an --exclude flag which allows users to explicitly exclude files and directories from the preview app and when building the preview app for deployment.

BREAKING CHANGES: This is a breaking change as it requires breaking changes in the preview app